The invention concerns a determination method for an analyte on a chromatographic test strip using particle-labelled binding partners and a corresponding test strip.
For some time chromatographic analytical elements or test strips have also been used to an increasing extent to detect analytes with the aid of analyte-specific binding partners. These test elements have been successfully used especially in immunoassays since a so-called bound/free separation can rapidly take place due to the chromatographic migration of the analyte solution. For this a labelled binding partner is bound directly or indirectly when it passes a capture reagent in amounts that depend on the amount of the analyte and can thus be determined in this manner. Such test strips and determination methods are described among others in EP-A-0 186 799, EP-A-0 291 194, EP-A-0 323 605 and EP-A-0 250 137.
Recently increasing use has been made of so-called directly labelled binding partners for detection since, in contrast to enzyme-labelled binding partners, their label can be detected directly without addition of an enzyme substrate. In this case labels are advantageous which can be seen with the naked eye, in particular particulate insoluble labels such as dyed latex, coloured sols and metal sols especially gold. In chromatographic immunoassays these direct labels are fixed by immobilized binding partners in a capture zone when the analyte is present and are measured visually as a measure for the presence of the analyte. These capture reagents are preferably accommodated in a small space as a line in order to achieve a higher concentration of the directly labelled binding partners. When an analyte is present a coloured line forms in the line-shaped capture zone which can be observed with the naked eye.
It has turned out that the human eye has difficulties in distinguishing whether a line has formed or not in the capture zone especially with low amounts of analyte. In particular when the lighting conditions are poor a colouration in the capture zone is not noticed and so a false-negative result is read.